GIS equipment, namely sulfur hexafluoride closed-type combination of electrical appliances, internationally known as the “gas-insulated switchgear” (Gas Insulated Switchgear) was born in the mid 1960s. It put substation primary equipments except transformer including circuit breakers, disconnectors, fast (ground) switch, current transformers, voltage transformers, arrester, bus (three phase or single phase), connecting pipe, transition elements and cable terminals in a fully enclosed metal shell. The medium for insulation and are quenching is 0.4˜0.6 MPa SF6 gas. With the continuous maturing of GIS technology, the area and volume of GIS equipment are getting smaller and the operation is more and more reliable. The failure rate and maintenance workload of GIS put into operation early are obviously lower than other types of switchgear. Therefore, in the transformation of urban network, GIS has been widely used.
With the rapid increase of GIS usage in China in recent years and the increase of GIS operation period in early time, the failure rate of GIS has a tendency to increase and is far higher than the GIS accident rate requirements of no more than 0.1 intervals/100*years proposed by IET.
GIS is made up of a number of electrical devices, but the fault situation is not the same as the failure of individual electrical equipment. And the failure rate is far lower than the failure rate of independent electrical equipment. Long time in high pressure environment has become a main failure cause of a lot of GIS. GIS equipment need to go through strict process control to ensure the quality of the operation of GIS. But many parts of the process may be a potential risk of GIS failure. According to the failure occurred in the manufacturing and installation aspects. Although GIS has a high operational reliability, the long-running GIS will inevitably have material deterioration, as well as loose or deformation in the connecting components under electromotive force. The types of GIS faults are various, but the common faults are relatively concentrated. According to the national GIS fault statistics, GIS fault can be divided into mechanical failure, insulation failure, secondary circuit failure, body leakage failure and other failures, in which insulation fault is the most common in partial discharge, and gas leakage is most common in mechanical failure. With the GIS running for a long time, under the influence of long-term vibration, the flange connection will loosen to cause the gas chamber to have the air leakage; At the same time, deterioration of the pot-type insulator will also lead to gas leakage. Once the live gas leakage part is no longer completely enclosed in the inert SF6 gas, the external contact will be affected by the external environment, and the reliability will be reduced. Therefore, real-time monitoring of gas leaks in GIS gas chambers is of great significance for timely detection of GIS anomalies and ensuring the normal operation of GIS.
At present, the status monitoring for GIS mainly focuses on monitoring the partial discharge fault of GIS, and forms many methods such as UHF method, ultrasonic method, gas analysis method and so on. And the monitoring technology is more and more mature. The researches on GIS mechanical faults are mainly focused on the monitoring of GIS actuators such as circuit breakers, isolating switches, earthing switches and so on. So far, GIS gas leak monitoring rely mainly on gas pressure of gauge gas chamber. However, gas pressure gauges are insensitive to small gas changes, and gas leakage has become more severe when gas pressure gauges change parameters. In addition, the current gas pressure gauge is still dependent on manual reading to found abnormal. Real-time is poor and efficiency is very low. Therefore, it is necessary to find a more reliable and simple gas leak detection method.